The present invention relates generally to the transfer of substrates typically used in the fabrication of electronic devices such as integrated circuits and flat panel displays. Specifically, the invention relates to an interface chamber such as a loadlock chamber used to transfer substrates from one environment to another environment in a processing system.
Vacuum processing systems are often used in the fabrication of integrated circuits and flat panel displays. For example, one typical vacuum processing system includes a centralized transfer chamber mounted on a monolith platform or mainframe structure. One or more process chambers are in communication with the transfer chamber via access ports and associated slit valves through which the substrates are transferred between the transfer chamber and the adjoining process chambers.
Substrates are passed through the system by a substrate handling robot disposed in the transfer chamber. The slit valves isolate the process chambers from each other and from the transfer chamber while substrates are being processed. The transfer chamber is typically held at a constant vacuum, while the process chambers may be pumped to a greater or lesser vacuum than the transfer chamber for performance of their respective processes. Afterward, the process chamber pressure returns to the level in the transfer chamber before opening the slit valve to permit access between the chambers.
The substrate handling robot disposed in transfer chamber typically retrieves one or more unprocessed substrates from one or more loadlock chambers connected to the transfer chamber and places the substrates in the process chambers. The loadlock chambers selectively cycle between the pressure level of the ambient environment and the pressure level in the transfer chamber to transition the substrates between atmospheric pressure and the vacuum environment of the transfer chamber. One type of loadlock chamber in widespread use has a relatively large volume and is capable of storing multiple substrates. Typically, thirteen to twenty-five substrates are stacked vertically in one or more substrate cassettes disposed in loadlock chambers. The substrate cassettes typically include a plurality of substrate supports spaced vertically to permit a substrate handling robot blade to reach under a substrate to remove or place a substrate. Substrates are typically loaded in and removed from the loadlock chamber by a staging robot at or near a front-end staging area, which is also often referred to as the xe2x80x9cfactory interface.xe2x80x9d
Typically, the factory interface area is maintained at or near ambient or atmospheric pressure. Accordingly, prior to transfer of substrates into or out of the loadlock chamber, the atmospheric volume within the loadlock chamber is usually vented to atmospheric pressure before opening the valves of the loadlock chamber. Similarly, before transfer of substrates between the loadlock chamber and the transfer chamber, the atmospheric volume within the loadlock chamber is usually evacuated to the low pressure maintained in the transfer chamber. Because of the sizable volume within typical loadlock chambers, it may take a relatively lengthy amount of time to vent and then evacuate the loadlock chamber before permitting access to the substrates by the substrate handling robot. This process may typically take approximately four (4) minutes to complete in some applications. During this time, the vacuum processing system may sit idle while awaiting the introduction of additional unprocessed substrates into the system.
It has been found that substantial production gains may be made by reducing the atmospheric volume within the loadlock chamber serving the transfer chamber. Accordingly, systems having single or dual substrate loadlock chambers have been developed to reduce venting and evacuation time within the loadlock process chamber, which has resulted in a reduction of process chamber idle time and an increase in production. Examples of such loadlock chambers include those described in application Ser. No. 137,324, filed Jun. 3, 1999 and application Ser. No. 505,901 filed Feb. 17, 2000 (having counterpart EP 1058291 published Dec. 6, 2000); and application Ser. No. 464,362, filed Dec. 15, 1999 (having counterpart EP 1109203 published Jun. 20, 2001), which are incorporated herein by reference.
A reduction in the number of substrates housed in the loadlock chamber often makes it desirable to increase the speed at which the substrates are transferred through the loadlock chamber. However in many applications it is desirable to heat the substrates prior to processing in the processing chambers. Heating the substrate may for example assist in degassing undesirable contaminant gasses such from the substrate prior to introducing the substrate into the main processing system. In those applications in which the substrate is heated in the loadlock chamber prior to processing, a shorter transition time through the loadlock chamber reduces the time available to heat the substrates in the loadlock chamber.
The present inventions are directed to, in one aspect, a method and apparatus for processing a semiconductor substrate in a system which includes a chamber having a valve such as a slit valve wherein the interior of the chamber is vented with a purge gas to a pressure greater than the pressure external to the valve to provide a positive pressure gradient between the chamber interior and the valve external pressure. Upon opening the chamber valve to permit a substrate to be loaded into or removed from the chamber, purge gas is continued to be admitted into the chamber interior while the chamber valve is open to maintain a positive pressure gradient while said chamber valve is open. In some applications, such a positive pressure gradient may be used to inhibit the passage of contaminant gasses from the exterior of the chamber to the interior while the slit valve is open.
Once the chamber valve is closed, the chamber may be pumped down to a lower pressure and heating of the substrate may be initiated. In one embodiment, the chamber may be a load lock chamber having a heater to degas the substrate. The chamber slit valve may provide access to a factory interface which is at ambient pressure. In some applications, it is appreciated that the degassing of a substrate in a load lock chamber may be initiated at higher pressures and thus earlier in completion of the pumping cycle where the admission of contaminant gasses is inhibited by a positive pressure gradient maintained when the slit valve to the factory interface is open.
There are additional aspects to the present inventions. It should therefore be understood that the preceding is merely a brief summary of some embodiments and aspects of the present inventions. Additional embodiments and aspects of the present inventions are referenced below. It should further be understood that numerous changes to the disclosed embodiments could be made without departing from the spirit or scope of the inventions. The preceding summary therefore is not meant to limit the scope of the inventions. Rather, the scope of the inventions is to be determined by appended claims and their equivalents.